Elsevier

Journal of Membrane Science

Volume 620, 15 February 2021, 118901
Journal of Membrane Science

Inkjet printed single walled carbon nanotube as an interlayer for high performance thin film composite nanofiltration membrane

https://doi.org/10.1016/j.memsci.2020.118901Get rights and content

Highlights

  • Formation of ultrathin active layer using SWCNT interlayer via inkjet printing.

  • TFC NF membrane with SWCNT interlayer exhibited high flux and high salt rejection.

  • Investigate SWCNT interlayer & printing parameters on NF membrane performances.

  • Role of SWCNT interlayer on ultrathin active layer formation via membrane autopsy.

Abstract

Inkjet printing process enables rapid deposition of inks with precise amount and location. Moreover, the process can be automated and provide control such as repetitive printing of the inks. Utilizing the advantageous features of the inkjet printing process, we demonstrate the synthesis of thin film composite (TFC) flat-sheet membrane for NF application where single walled carbon nanotube (SWCNT) was deposited via an inkjet printing process, acting as an interlayer between the polyamide (PA) selective layer and polyethersulfone (PES) MF membrane support. By controlling the number of SWCNT printings on the PES membrane, we investigated how the SWCNT interlayer thickness influences the formation of PA selective layer. The best membrane performance was achieved from the TFC membrane synthesized using 15 cycles of SWCNT printing, where both high water flux (18.24 ± 0.43 L m−2 h−1 bar−1) and the high Na2SO4 salt rejection (97.88 ± 0.33%) rates were demonstrated. SWCNT interlayer provided highly porous, interconnected structure with uniform pore size distribution which led to the formation of a defect-free ultrathin PA selective layer. Designing of TFC membrane using the SWCNT deposition via inkjet printing is the new approach and successfully demonstrated the significant improvement in the NF membrane performances.

Introduction

Thin film composite (TFC) membranes are conventionally synthesized by interfacial polymerization (IP) which forms a thin active layer on top of a microfiltration (MF) or ultrafiltration (UF) membrane substrates, where two different monomers of m-phenylenediamine (MPD) or piperazine (PIP) and trimesoylchloride (TMC) are commonly utilized to synthesis a polyamide (PA) active layer [[1], [2], [3]]. Both water permeability and selectivity of the membranes are most crucially dependent on PA active layer properties, while porous membrane support provides a robust mechanical support for PA selective layer. To this date, nanofiltration (NF) membranes composed of a thin film PA layer on top of UF membrane have been successfully commercialized and currently being used in wide range of applications in desalination and wastewater treatments. However, there are still challenges remain when they are implemented in the real field, due to their trade-off dilemma between the intrinsic solvent permeability and solute selectivity [4].

An ideal NF membrane needs to exhibit both high water permeability and high removal rate of various dyes or multivalent salts and other contaminants [5]. It is well known that, the thickness of PA selective layer is inversely proportional to the solvent permeability. Therefore, a desired PA layer structure can be achieved by fabricating an ultra-thin selective layer which is less than 100 nm in thickness whereas conventional TFC PA membranes are composed of 200–300 nm thin PA active layer with 150–300 μm porous support layer. Importantly, properties of the PA layer could significantly be influenced by structure and the surface property of a porous support substrate [[6], [7], [8], [9]]. Recently, various efforts have been made to improve the membrane performances (water flux and selectivity) and membrane stabilities. One of a notable strategy is by addition of an interlayer between the PA active layer and the microporous support substrate. For example, Livingston et al. successfully synthesized an ultrathin PA active layer with a thickness of 10 nm by utilizing a porous cadmium hydroxide nanostrands as interlayer which covered the surface of polyimide ultrafiltration support membranes and a follow up IP reaction [6]. The smooth and uniform nanoporous structure of the nanostrands interlayer enabled the formation of a defect-free and ultrathin PA active layer, which achieved outstanding improvement in solvent permeability while retaining its excellent salt rejection capability. Inspired by this study, Zhu and co-workers used polydopamine (PDA) coated single-walled carbon nanotube (SWCNT) as an interlayer which was deposited via a simple vacuum filtration technique [10]. This hydrophilic and smooth PDA/SWCNT interlayer induced the formation of defect-free, highly crosslinked PA selective layer with a thickness of 12 nm, which improved the NF membrane performances compared to the interlayer free TFC membrane.

As noted in previous studies, deposition of interlayer using different nanomaterials played an important role in improving the NF membrane performances [[7], [8], [9], [10], [11], [12], [13], [14], [15]]. However, those conventional approaches such as vacuum filtration, dip-coating, spin-coating and layer-by-layer (LBL) methods in deposition of materials, as an interlayer for TFC membrane fabrications, often lead to poor controllability of the deposited material surface properties or limited in scalability and in some cases producing unwanted wastes [7,9,10,16,17]. Meanwhile, inkjet printing process could be a promising candidate which can enable the deposition of nanomaterial based interlayer uniformly. Inkjet printing is a versatile tool which can deliver precise and rapid deposition of organic, polymeric materials and nanomaterials at scale for various applications [[18], [19], [20], [21], [22]]. Moreover, conventional routes in depositing polymers or nanomaterials often generated chemical and nanomaterial wastes which remains a significant challenge. These material wastage issues can be minimized when depositing materials via inkjet printing process as precise amount of material deposition is possible in this process.

Therefore, such features of the inkjet printing process and inspired from the successful implementation of inkjet printing process in other applications, this work aims to take the advantage of the inkjet printing technology in membrane manufacturing, which will deliver deposition of uniform nanomaterial interlayer with good controllability for high performing TFC membrane synthesis. In general, inkjet printing process enable the deposition of picoliter (2–30 pL/drop) scale of liquid drops through the number of nozzles from a print-head, with frequencies of up to 2000 drops s−1 per nozzle [23]. Moreover, inkjet printing process provided precise control in positioning of the polymer solution deposition at a high speed [24]. Due to these advantages of inkjet printing technique, recent studies successfully demonstrated the uniform coating of nanomaterials such as graphene, graphene oxide, metal organic frameworks (MOF) and CNTs on a paper substrate for patterning of conductive materials [19,[25], [26], [27]]. Furthermore, one study has successfully demonstrated the deposition of ultrathin and uniform graphene oxide layer on a polymeric support membrane to synthesize a NF membrane for water purification [28]. As such, use of inkjet printing in membrane manufacturing require further exploration and demonstrations in diverse membrane synthesis applications to fulfill its potential in bringing the efficient, precision controlled and scalable membrane manufacturing into reality.

In this study, we demonstrate the deposition of uniform, smooth SWCNT layer via inkjet printing process to serve as an interlayer between the PA active layer and PES MF membrane which is first demonstration for NF application. Multiple number of SWCNT printings on the PES membrane were conducted to investigate how SWCNT interlayers influenced the formation of PA active layer using various membrane characterizations. Moreover, the performance of fabricated TFC NF membranes were evaluated by water permeability and salt rejection tests to find an optimal fabrication condition. The different surface characteristics of SWCNT interlayers induced by different number of inkjet printing and the respective formation of PA layer was further investigated. Our studies shed light on the control of PA selective layer in TFC membrane by introducing the uniform, nanomaterial based interlayer and demonstration the further use of inkjet printing process in membrane manufacturing which plays a crucial role in synthesis of high performing TFC membrane.

Section snippets

Materials and chemicals

Hydrophilic PES microfiltration (MF) membrane filter with a pore size of 0.22 μm was used as membrane support (Sterlitech, USA). Carboxylated SWCNT (SWCNT, Purity: >95 wt%, outer diameter (OD): 1–2 nm) powder with a short length (1–3 μm) was purchased from Jiangsu XFNANO Materials Tech CO., Ltd, China. Sodium dodecyl sulfate (SDS, ≥99.9%) from Sigma-Aldrich was used as the surfactant for SWCNT dispersion. For PA active layer formation, piperazine (PIP, 99% purity) and trimesoyl chloride (TMC,

Effect of SWCNT deposition via inkjet printing on PES MF membrane supports

The SWCNT interlayer deposition on the PES MF support membrane was conducted via inkjet printing technology. The prepared SWCNT ink was smoothly printed on the membrane substrate and did not observe any blockage of nozzles in the cartridge head during the whole printing experiments (See Supplementary Video S1). The effects of coated SWCNT layer on the properties and morphology changes of PES membrane surface were investigated as these two parameters strongly influence the formation of PA layer

Conclusions

A high performance TFC NF membrane with ultrathin PA active layer was successfully synthesized by using SWCNTs as an interlayer between the PA active layer and PES MF membrane support. We first introduced a potential application of inkjet printing technology to deposit SWCNT ink on PES MF membrane to utilize them as an interlayer. SWCNT ink printed over 10 cycles efficiently modified the surface morphology of PES MF support membrane by reducing surface pore size and roughness, thereby achieving

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the research support of the Australian Research Council (ARC) Discovery Projects (DP210101361). D.H.S acknowledges the support of Chancellor's postdoctoral research fellow scheme from the University of Technology Sydney.

References (32)

  • M.J. Park et al.

    Graphene oxide incorporated polysulfone substrate for the fabrication of flat-sheet thin-film composite forward osmosis membranes

    J. Membr. Sci.

    (2015)
  • M.J. Park et al.

    Hydrophilic polyvinyl alcohol coating on hydrophobic electrospun nanofiber membrane for high performance thin film composite forward osmosis membrane

    Desalination

    (2018)
  • X. Hao et al.

    Calcium-carboxyl intrabridging during interfacial polymerization: a novel strategy to improve antifouling performance of thin film composite membranes

    Environ. Sci. Technol.

    (2019)
  • S. Karan et al.

    Sub-10 nm polyamide nanofilms with ultrafast solvent transport for molecular separation

    Science

    (2015)
  • Y. Liang et al.

    Graphene quantum dots (GQDs)-polyethyleneimine as interlayer for the fabrication of high performance organic solvent nanofiltration (OSN) membranes

    Chem. Eng. J.

    (2020)
  • P. Gorgojo et al.

    Ultrathin polymer films with intrinsic microporosity: anomalous solvent permeation and high flux membranes

    Adv. Funct. Mater.

    (2014)
  • Cited by (61)

    View all citing articles on Scopus
    1

    These authors contributed equally in this work.

    View full text